I distinctly remember one occasion when I was instructing a group of software engineers on the topic of "agile planning", and I started drawing a picture of the "cone of uncertainty".
And I stopped dead in my tracks.
Because I'd just realized I hadn't the foggiest idea what I was talking about, or how I'd know if it made sense. I was just parroting something I'd read somewhere, and for once trying to explain it wasn't helping me understand it better, it was just making me confused. And all I wanted to say anyway was "don't trust estimates made at the beginning of a project".
Fortunately nobody noticed (that often happens, and is a topic in its own right), I moved on, stopped using that picture and mostly forgot about it.
This was a few years back, and I like to think that in the meantime I've traversed the valley that lies behind Mt Stupid, and am now ready to start talking about it again. In particular what scares me - you'll be scared too if you google for "software" and "cone of uncertainty" - is how many people in the profession are still stuck on the summit: willing to opine at length about the Cone, without an inch of critical distance from what they're quoting. Is it conceptual, speculative, empirical; if the latter, how well supported? People quoting it don't know and don't care.
I rather like the term "cone of uncertainty." It seems like a spell a third level wizard (or perhaps a junior year philosophy student) could cast.
A little knowledge is a dangerous thing, not sure what the official name for this particular cognitive bias is (feel free to enlighten me). Probably most of us can recognize that feeling of enlightenment after learning a bit of something new and exciting, and not realizing yet how far it is from the mastery of the subject. I suspect that learning the LW brand of rationality is one of those. (Incidentally, if the words "LW brand of rationality" irked you, because you think that there is only one true rationality, consider how close you might be to that particular summit of Mt. Stupid.) See also the last bullet point in the linked comic strip.
As an exercise in rationality, I suggest people post personal accounts of successfully traversing Mt.Stupid, or maybe getting stuck there forever, never to be heard from again. Did you find any of the techniques described in the sequences useful to overcome this bias, beyond the obvious of continuing to learn more about the topic in question? Did you manage to avoid turning Mt.Stupid into the Loggerhead range?
My example: I thought I was great at programming fresh out of college, and ready to dispense my newly found wisdom. Boy, oh boy, was I ever wrong. And then it happened again when I learned some more of the subject on the job...